There aren't too many voice performances that are considered iconic, in the way that some of Idol's greatest moments were. (Adam Lambert's "Mad World" or Fantasia's "Summer Time" ) Performances that expanded past the show. Melanie's blind is one of the few that did.

No, it's not the most amazing vocal in the world. But the melody changes and arrangement are both remarkable and memorable. Melanie's cover has not only gone viral in a few different mediums (Tumblr, Facebook etc..), but it's well known enough that covers of her cover appear in other shows. (Either other reality television competitions or other shows in general.)